WASHINGTON – The Whydah originally set sail as a slave ship prior to being captured by pirates. But the pirates and the treasure all sank before the captain reached land for a rendezvous with his girlfriend, a condemned witch.

This twisting and tragic story – supplemented by artifacts and loot – is on display at the National Geographic Museum in an exhibit called “Real Pirates: The Untold Story of the Whydah from Slave Ship to Pirate Ship.”

Visitors can expect to see cannons, hand grenades, treasure and disturbing artifacts from the ship’s roll in slave trade, all on display through Sept. 2.

“What people have to really understand when they come to see this is that they’re seeing the only pirate treasure that’s ever been discovered in the world,” says Barry Clifford, the explorer who found the wreckage in 1984.

“Anybody who had ever walked the beach and thought of finding pirate treasure – this is the only place in the world they can see it,” he says. “It’s the only documented pirate treasure that’s ever been excavated.”

The incredible story of the Whydah begins in London in 1715.

The three-masted, 300-ton galley was said to be the most advanced of its time. It was built as a slave ship and in 1717 the Whydah transported captives from the west coast of Africa to be sold in Jamaica.

Afterward as the ship and its crew headed back to England with the money, they were taken over by pirates, including Sam Bellamy, one of the most notorious pirates of his day.

“This was the 50th ship that they had captured,” Clifford says. “Because the Whydah was a new ship, [Bellamy] converted it into his own ship.”

Bellamy decided at that point to head up to Massachusetts, where legend has it he was going to reunite with his girlfriend, Maria Hallett.

“Unbeknownst to him, she had been condemned as a witch,” Clifford recounts.

Just the same, she didn’t know that he had become a pirate.

As the pirates neared the coastline, they were caught in a horrific nor’easter. The Whydah and treasure collected from 50 ships sank on the back side of Cape Cod, in a place called the Graveyard.

The story served as a fantastic legend until its discovery in 1984. Now, artifacts such as swords, muskets and personal items from the ship are on display in the museum’s 17th Street gallery.